"Ah sinful nation, a people laden with iniquity, a seed of evildoers, children that are corrupters: they have forsaken the LORD, they have provoked the Holy One of Israel unto anger, they are gone away backward."
In verse 4, the Lord goes into more detail about the crimes / sins of which his children are guilty. They are a "sinful nation, a people laden with iniquity." I like this imagery. "Laden" means "burdened, encumbered, weighed upon heavily or oppressively." Truly, our sins do weigh heavily upon our souls and burden us with a heavy yoke. Through our sins we are brought into a spiritual bondage, the captivity of the devil, the chains of hell. It is grievous to be borne. It is to this burden of sin which the Lord speaks in Matthew 11:28-30: "Come unto me, all ye that labour and are heavy laden, and I will give you rest. Take my yoke upon you, and learn of me; for I am meek and lowly in heart: and ye shall find rest unto your souls. For my yoke is easy, and my burden is light."
Verse 4 continues: "a seed of evildoers," --meaning that this wickedness has continued through many generations. Both parents and children are evildoers.
"...children that are corrupters" --the definition of "corrupt" is "to change from good to bad in morals, to degrade with unsound principles or moral values, to alter from the original or correct form or version." Throughout history the world has corrupted that which is sacred and sought their own version of morality. I think the devil is the corrupter of all that which is good. He takes the truth and twists it or changes it just enough that it becomes corrupted and leads men astray. He tempts each of us to use our God given agency to "decide for ourselves" those parts of the gospel which we will believe, those commandments which we will follow, and lulls us into thinking that we don't have to accept certain things or submit our whole will to the Lord. Thus pride and iniquity lead men to become corrupters of that which God has proclaimed.
"...they have forsaken the LORD" --the definition of "forsake" is "to renounce or turn away from entirely." In 1 Kings 11:33, we learn some of the ways the Israelites had forsaken the Lord: "Because that they have forsaken me, and have worshipped Ashtoreth the goddess of the Zidonians, Chemosh the god of the Moabites, and Milcom the god of the children of Ammon, and have not walked in my ways, to do that which is right in mine eyes, and to keep my statutes and my judgments, as did David his father." They had forsaken the Lord by worshipping false gods and by not keeping the commandments of the Lord. (There will be more detail into this later in the chapter.)
"...they have provoked the Holy One of Israel unto anger" --In Doctrine & Covenants 63:32-33 it says: "I, the Lord, am angry with the wicked; I am holding my Spirit from the inhabitants of the earth. I have sworn in my wrath, and decreed wars upon the face of the earth, and the wicked shall slay the wicked, and fear shall come upon every man." In 2 Nephi 15:25 it says: "Therefore, is the anger of the Lord kindled against his people, and he hath stretched forth his hand against them, and hath smitten them; and the hills did tremble, and their carcasses were torn in the midst of the streets. For all this his anger is not turned away, but his hand is stretched out still." Why was the Lord angry? The previous verse (2 Nephi 15:24) says, "...because they have cast away the law of the Lord of Hosts, and despised the word of the Holy One of Israel."
"...they are gone away backward." --In other words, they need to turn around and face God. Instead of forsaking the Lord, they should be forsaking sin. They need to repent, or turn around, turn from their sin. The phrase, "gone away backward" denotes that they are not just stagnate in their turning away, but are regressing. This is the opposite of progression. Instead of continually improving, they are going backward losing even that small part they may have once had. This principle is echoed in D&C 1:33. "And he that repents not, from him shall be taken even the light which he has received; for my Spirit shall not always strive with man, saith the Lord of Hosts."
This is also echoed in 2 Peter chapter 2. In fact verses 15 & 19-22 are a good summary of those things we've discussed above: "Which have forsaken the right way, and are gone astray, following the way of Balaam the son of Bosor, who loved the wages of unrighteousness;...While they promise them liberty, they themselves are the servants of corruption: for of whom a man is overcome, of the same is he brought in bondage. For if after they have escaped the pollutions of the world through the knowledge of the Lord and Saviour Jesus Christ, they are again entangled therein, and overcome, the latter end is worse with them than the beginning. For it had been better for them not to have known the way of righteousness, than, after they have known it, to turn from the holy commandment delivered unto them. But it is happened unto them according to the true proverb, The dog is turned to his own vomit again; and the sow that was washed to her wallowing in the mire."